1. Field of the Invention
This invention relates to compounds which selectively bind to brain dopamine receptor subtypes. More specifically, it relates to 1-(N'-(arylalkylaminoalkyl)) aminoisoquinolines and to pharmaceutical compositions comprising such compounds. It further relates to the use of such compounds in treating various neuropsychochological disorders.
2. Description of the Related Art
Schizophrenia or psychosis is a term used to describe a group of illnesses of unknown origin which affect approximately 2.5 million people in the United States. These disorders of the brain are characterized by a variety of symptoms which are classified as positive symptoms (disordered thought, hallucinations and delusions) and negative symptoms (social withdrawal and unresponsiveness). These disorders have an age of onset in adolescence or early adulthood and persist for many years. The disorders tend to become more severe during the patient's lifetime and can result in prolonged institutionalization. Within the United States of America, approximately 40% of all hospitalized psychiatric patients suffer from schizophrenia.
During the 1950's physicians demonstrated that they could successfully treat psychotic (schizophrenic) patients with medications called neuroleptics. This classification of antipsychotic medication was based largely on the activating (neuroleptic) properties of the nervous system by these drugs. Subsequently, neuroleptic agents were shown to increase the concentrations of dopamine metabolites in the brain. This finding suggested that altered neuronal firing of the dopamine system contributed in some way to the aberrant behavior observed in schizophrenic patients. Additional evidence indicated that dopamine could increase the activity of adenylate cyclase in the corpus striatum, an effect reversed by neuroleptic agents. Thus, cumulative evidence from these and later experiments strongly suggested that the neurotransmitter dopamine was involved in schizophrenia.
One of the major actions of antipsychotic medication is the blockade of dopamine receptors in brain. Several dopamine systems appear to exist in the brain and at least five classes of dopamine receptors appear to mediate the actions of this transmitter. These dopamine receptors differ in their pharmacological specificity and were originally classified on the basis of their ability to bind various dopaminergic ligands.
The butyrophenones are a class of drugs containing many potent antipsychotic drugs. Perhaps the most prominent member of this class of compounds is the antipsychotic drug haloperidol (chemical name). Haloperidol binds relatively weakly at the major dopamine receptor subtype which activates adenylate cyclase (commonly classified as the D.sub.1 dopamine receptor). In contrast, haloperidol displayed binding affinity at a dopamine receptor subtype which suppressed the activity of adenylate cyclase (commonly classified as D.sub.2 receptors) in the subnanomolar range.
Recently, three additional dopamine receptor subtypes have been identified using the often congruent sciences of receptor pharmacology and molecular biology. These new dopamine receptors have been labeled as D3, D4, and D.sub.5. The D.sub.3 and D.sub.4 subtypes are pharmacologically related to the D.sub.2 receptor via their ability to suppress the activity of adenylate cyclase. Conversely, the D.sub.5 receptor is classified as a "D.sub.1 like" dopamine subtype through its ability to stimulate cyclase activity.
Recently, a new group of drugs (such as sulpiride and clozapine) have been developed with a lesser incidence of extrapyramidal side effects (EPS) than classical neuroleptics. In addition, there is some indication that they may be more beneficial in treating negative symptoms in some patients. Since all D.sub.2 blockers do not possess a similar profile, hypotheses underlying the differences have been investigated. Major differences have been detected in the anticholinergic actions of these drugs. It has also been suggested that the dopamine receptors in motor areas may differ from those in the limbic areas which are thought to mediate the antipsychotic responses. The existence of the D.sub.3, D.sub.4 and D.sub.5 and other as yet undiscovered dopamine receptors may contribute to this profile. Some of the atypical compounds possess similar activity at D.sub.2, D.sub.3 and D.sub.4 receptors.
Using molecular biological techniques it has been possible to clone cDNAs coding for each of the pharmacologically defined receptors. There are at least two forms of D1 which have been identified as D.sub.1 and D.sub.5, and two forms of D.sub.2, identified now as D2 and D.sub.4 dopamine receptors. In addition, there is at least one form of D.sub.3 dopamine receptor.
The therapeutic effect of conventional antipsychotics, known as neuroleptics, is generally believed to be exerted through blockade of dopamine receptors. However, neuroleptics are frequently responsible for undesirable extrapyramidal side effects (EPS) and tardive dyskinesias, which are attributed to blockade of D.sub.2 receptors in the striatal region of the brain. The dopamine D.sub.4 receptor subtype has recently been identified (Van Tol, H. H. et al., Nature, 1991, 350, 610). Its unique localization in limbic brain areas and its differential recognition of various antipsychotics suggest that D.sub.4 receptor plays a major role in the etiology of schizophrenia. Thus, selective D.sub.4 antagonists are considered effective antipsychotics free from the neuroglogical side effects displayed by conventional neuroleptics.
U.S. Pat. Nos. 5,602,168: 5,602,168 and 5,656,632, describe aminoisoindoles useful in treating neuropsychological disorders.